Carnegie Effective Speaking

According to the Wikipedia page on Dale Carnegie, One of the core ideas in his books is that it is possible to change other people’s behavior by changing one’s behavior toward them. I concur. I hold no animosity toward any of you, but I’d be downright friendly if you bought a book safe from me. Carnegie was a way better salesman than me. I found this interesting on his page as well, this is the first and last sentence from the second paragraph of his bio: After saving $500 (about $12900 today), Dale Carnegie quit sales in 1911…and by 1914, he was earning $500 (about $12000 today) every week. Are we to assume that today’s dollar dropped in value that much in the time that paragraph was written, or that its value in the early 1900s did? Could just be a typo.